In recent years, the desire to measure hand and finger motion by use of an instrumented glove has become increasingly more popular. Applications which employ such an instrumented glove include: virtual reality, telerobotics, medical hand-function evaluation, music generation, graphical character animation, and the like. One sensing technique which may be used to transduce joint position is a bend sensor, i.e., a sensor which is placed in juxtaposition to a joint and changes its output signal in response to the amount of bending of that joint.
For instrumented glove applications which benefit from knowledge of the position of the various parts of the hand, such as the phalanges of the fingers, in addition to joint angles directly measured, it is desirable to apply the joint angle measurements to a mathematical model of the hand geometry. By applying the measured joint angles to a hand model geometry, and incorporating knowledge of the anatomical structure of the skin and tissue of the hand and thumb, any of a variety of critical points on the hand and thumb at locations not explicitly measured may be calculated.
One desirable application, which makes use of the points on the hand calculated from the hand model, is to render a graphical "virtual" hand on a computer screen which mirrors the position and motion of the physical hand which joints are being sensed. Such a virtual hand may then interact with graphical virtual objects on the computer, where the actions of the virtual hand are controlled by a user's physical hand. Similarly, the points on the hand as calculated from the hand model may also be used to control an anthropomorphic robotic hand, which might be at a nearby or distant location, or located in an undersea or otherwise hazardous environment. Thereby, the robotic hand can be controlled in a human-like fashion by measurements from a physical hand, and where the robotic hand may be used to manipulate heavy or hazardous materials.
To help refer to the various joints and the complex movements of the hand, FIG. 1 is provided, which depicts the anatomical definitions of various joints and bones of the hand. FIG. 6 provides that the instantaneous center of rotation of a physical hand joint is modeled as a hinged joint, where the hinge axis position is constant. In referring to specific joints and links in FIG. 6, it should be understood that the figure is exemplary of typical joint-link constructions of the fingers and hand. Any two joints, such as 600 and 601, may be joined by a link 602, where in certain instances, the link represents one or more physical bone segments 603. Each fingertip 604 is also joined to the nearest joint 600 by a link 605. The angles 606 of joints (e.g., 600) may be measured by goniometers. Using the joint angle information and the kinematic joint-link model of the hand, the position and orientation of various links may be determined. Knowing the position of the bone 603, and using an anatomical model of the bone and surrounding tissue 607 and 608 relative to the link 602, by applying the information to a particular bone of the fingers or hand, we can calculate the position of any point internal to and on the surface 608 of the fingers and hand.
The flexure of the metacarpophalangeal joints, proximal interphalangeal joints and distal interphalangeal joints of the index, middle, ring and small fingers may be modeled in a simple fashion by a single axis of rotation. The metacarpophalangeal joint of each of these four fingers may also be modeled as including an abduction axis which lies normal to the plane defined by the flexure axis and the axis of the metacarpal bone. The flexure of the proximal and distal interphalangeal joints of the thumb may be similarly modeled by a single axis. The articulation of the trapeziometacarpal joint of the thumb (also referred to as the thumb metacarpocarpal joint) is not as simple, and is, in fact, quite complex. By observing the structure of the joint we see it is similar to a saddle joint. It is the measurement and characterization of this complex motion of the thumb which constitutes the substance of this invention.